Softening synthetic rubber



Patented Aug. 3, 1943 2,325,979 SOFTENING SYNTHETIC RUBBER Donald V. Sarbach, Ouyahoga Falls,

Ohio, assignor to The B. F. Goodrich Company, New York N. Y.. a corporation of New York No Drawing. Application March Serial No. 885,142

Claims.

This invention relates to the softening of synthetic rubber and to a new class of softeners which produce a great increase in plasticity when incorporated in unvulcanized synthetic rubber.

The softening of synthetic rubber has in general presented problems not encountered in the softening of natural rubber due to different behavior on mill rolls, incompatibility of synthetic rubber with certain softening materials commonly employed in natural rubber and other differences in properties. While the problem of satisfactorily softening synthetic rubber has been particularly diificult in the case of copolymers of butadiene and acrylonitrile, other synthetic rubbers prepared by the polymerization of conjugated dienes have also presented problems. The difiiculty has been increased by the fact that softeners for one type of synthetic rubber do not in all cases function similarly in other types of synthetic rubber. Even varying the proportions of the monomers in the mixtures employed to form copolymers has necessitated the search for new softeners for the synthetic rubber prodnet.

I have discovered a new class of softeners which may be employed to soften any of the synthetic rubbers prepared by the polymerization of conjugated butadienes, either alone or in the presence of other polymerizable materialsr These new softeners are compounds having the structural formula sired, as a practical matter, compounds containordinarily employed.

The preferred class of softeners is the tri-alkoxyalkyl phosphates such as tri-butoxyethyl phosphate, tri-ethoxyethyl phosphate, tri-methoxyethyl phosphate, tri-ethoxypropyl phosphate,

etc., although other classes such as the tri-aryloxyalkyl phosphates such as tri-phenoxyethyl phosphate and the tri-alkoxyalkoxyalkyl phosphates such as tri-butoxyethoxyethyl phosphate may be employed if desired. Compounds such as butoxyethyl phosphate which may be prepared from mixtures of partially substituted glycols may also be employed.

The softeners of rubber.

As a specific example of this invention, 50 parts of tri-butoxyethyl phosphate were incorporated together with conventional compounding ingredients in parts of a synthetic rubber prepared by the copolymerization in aqueous emulsion of 55 parts of butadiene and 45 parts of acrylonitrile.

be incorporated was obtained by incorporating an equal weight of tri-butoxyethyl phosphate with a synthetic rubber prepared by the copolymerization in aqueous emulsion of 55 parts of butadiene and 45 parts of acrylonitrile. Softeners belonging to this same class have also been successfully employed to soften compolymers of butadiene and methyl methacrylate and copolymers of butadiene and styrene.

The softeners herein described may be employed in conjunction .with synthetic rubber prepared by the polymerization of a conjugated butadiene such as butadiene-1,3 which is commonly called butadiene, isoprene, chloroprene, piperylene, 2,3-dimethylbutadiene, ec., alone or in admixture with each other or with oleflnic monomers copolymerizable therewith such as styrene, vinyl benzene,

isobutylene, acrylonimethoxyethyl ethoxyethyl tions and modifications are within the spirit and scope of the invention as defined in the appended claims.

I claim:

1. A composition of matter comprising a rubbery polymer of a conjugated butadiene and, as a softener therefor, a compound of the formula Ri"-(Rl' )n wherein R1 is a monovalent hydrocarbon group, R2 is a bivalent hydrocarbon group and n is an integer.

2. A composition of matter comprising a rubbery polymer of a conjugated butadiene and, as a softener therefor, a tri-alkoxyalkyl phosphate.

3. A composition of matter comprising a rubbery copolymer of a conjugated butadiene and a copolymerizable mono-olefinic compound and, as a softener therefor, a compound of the formula ai-om-o),

l (R7 O)n'-P=O RiO(R|- )n wherein R1 is a monovalent hydrocarbon group,

Re is a bivalent hydrocarbon group and n is an integer less than four.

4. A vulcanized composition comprising a rubbery copolymer of butadiene-1,3 and a copolymerizable mono-oleflnic compound and, as a softener therefor, a tri-aikom'alkyl phosphate.

5. A composition of matter comprising a rubbery copolymer of butadiene-1,3 and acrylonitriie and, as a softener therefor, a tri-alkoxyalkyl phosphate. 7

6. A composition of matter comprising a rubbery copolymer of butadiene-1,3 and methyl methacrylate and, as a softener therefor, a trialkoxyalkyl phosphate.

'7. A composition of matter comprising a rubbery copolymer of butadiene-1,3 and styrene and, as a softener therefor, a tri-alkoxyalkyl phosphate.

8. The composition of claim!) wherein the softener is tri-butoxyethyl phosphate.

9. The composition of claim 6 wherein the softener is tri-butoxyethyl phosphate.

10. The composition of claim 7- wherein the softener is tri-butoxyethyl phosphate.

DONALD V. SARBACH. 

